Time-variable gravity field recovery from reprocessed GOCE precise science orbits

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https://doi.org/10.48350/152967 | downloaded: 31.1.2022ombein, D. Arnold, A. Jäggi: Time-variable gravity field recovery from reprocessed GOCE precise science orbits COSPAR Scientific Assembly, Jan 28 –Feb 04, 2021

Astronomical Institute University of Bern

Sidlerstrasse 5 CH-3012 Bern

Time-variable gravity field recovery from reprocessed GOCE precise science orbits

Thomas Grombein, Daniel Arnold, Adrian Jäggi

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d, A. Jäggi: Time-variable gravity field recovery from reprocessed GOCE precise science orbits c Assembly, Jan 28 –Feb 04, 2021

Introduction

• ESA’s satellite mission GOCE (2009 – 2013)

– Gravity Field and Steady-State Ocean Circulation Explorer – Sun-synchronous orbit, mean altitude ~255 km

– Core instrument: Gravity gradiometer (consisting of six accelerometers)

• Satellite-to-Satellite Tracking (SST)

– Two dual-frequency GPS receivers – Primary instrument for

• GPS-based orbit determination

• GPS-based gravity field recovery

• Issues with operational GOCE orbits (Jäggi et al., 2015)

– Orbit positions affected by large ionospheric changes – Limitations for (time-

variable) gravity field

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ombein, D. Arnold, A. Jäggi: Time-variable gravity field recovery from reprocessed GOCE precise science orbits COSPAR Scientific Assembly, Jan 28 –Feb 04, 2021

GOCE Reprocessing Campaign at AIUB

• Reprocessing of GOCE Precise Science Orbits (PSO)

– Bernese GNSS software using reprocessed GPS products (Sušnik et al., 2020) – GPS data weighting strategy to mitigate ionospheric effects (Schreiter et al., 2019)

➢ Unweighted and weighted reprocessed PSO

• Gravity field recovery (Celestial Mechanics Approach)

– 1-sec reprocessed kinematic GOCE positions + covariance information – Use of GOCE accelerometer (ACC) data as part of the force model

Reprocessed PSO (unweighted)

Reprocessed PSO (weighted)

Reprocessed PSO (weighted) + ACC data

• Computed gravity field solutions:

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GPS-based gravity field recovery with GOCE

• Quality of bi-monthly gravity field solutions

Geoid height differences

w.r.t. ITSG-Grace2018

(300 km Gauss-filtered)

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GPS-based gravity field recovery with GOCE

• Quality of bi-monthly gravity field solutions

Mean total electron content

[TECU]

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GPS-based gravity field recovery with GOCE

• Quality of bi-monthly gravity field solutions

Geoid height differences

w.r.t. ITSG-Grace2018

(300 km Gauss-filtered)

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weighted PSO

unweighted PSO

Zonal and near zonal SHCs excluded

Improvements in long-term solutions

• Geoid height differences • Difference degree amplitudes

Zonal and near zonal

SHCs excluded

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unweighted PSO

Zonal and near zonal SHCs excluded

Improvements in long-term solutions

• Geoid height differences • Difference degree amplitudes

Zonal and near zonal SHCs excluded

weighted PSO

+

ACC

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Time-variable gravity field recovery

Trend term Cosine term ← Annual variations → Sine term

• Set up of (static) SH coefficients up to d/o 120

• Parameter transformation on the level of normal equations (for coefficients up to d/o 10)

Offset

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Time-variable gravity field recovery

• Reference values from GRACE K-band data (a posteriori fit of monthly ITSG-Grace2018 solutions)

Cosine

Equivalent water

Sine Trend

• Set up of (static) SH coefficients up to d/o 120

• Parameter transformation on the level of normal equations (for coefficients up to d/o 10)

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weighted PSO unweighted PSO

without ACC data

with ACC data

Estimated trends from GOCE (Nov 2009 − Oct 2013)

Equivalent water heights

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Time-variable gravity field signals (Nov 2009 − Oct 2013)

Cosine Sine

Trend

GRACE GPS GOCE

GPS

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Summary

Solution Trend [cm/year]

Cosine [cm]

Sine [cm]

GOCE-GPS 1.27 1.44 1.37

GRACE-GPS 1.87 1.35 1.01

RMS values w.r.t.

ITSG-Grace2018

• Complete reprocessing of the GOCE Precise Science Orbits (PSO)

• Improved GPS-based gravity field recovery based on reprocessed PSO

• Time-variable gravity field recovery from reprocessed PSO

– Major time-variable signals can be recovered from about 4 years of GOCE-GPS data – Use of GOCE accelerometer data is crucial to derive meaningful linear trends

– Temporal variations obtained from GOCE are comparable to those from GRACE-GPS data

© ESA

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Summary

Solution Trend [cm/year]

Cosine [cm]

Sine [cm]

GOCE-GPS 1.27 1.44 1.37

RMS values w.r.t.

ITSG-Grace2018

• Complete reprocessing of the GOCE Precise Science Orbits (PSO)

• Improved GPS-based gravity field recovery based on reprocessed PSO

• Time-variable gravity field recovery from reprocessed PSO

– Major time-variable signals can be recovered from about 4 years of GOCE-GPS data – Use of GOCE accelerometer data is crucial to derive meaningful linear trends

– Temporal variations obtained from GOCE are comparable to those from GRACE-GPS data

References

Jäggi A, Bock H, Meyer U, Beutler G, van den IJssel J (2015): GOCE: assessment of GPS-only gravity field determination. Journal of Geodesy 89(1):33–48, DOI:10.1007/s00190-014-0759-z Schreiter L, Arnold D, Sterken V, Jäggi A (2019): Mitigation of ionospheric signatures in Swarm GPS gravity field estimation using weighting strategies. Annales Geophysicae 37(1):111–127, DOI:10.5194/angeo-37-111-2019

Sušnik A, Grahsl A, Arnold D, Villiger A, Dach R, Beutler G, Jäggi A (2020): GOCE: Validation of the EGSIEM-REPRO GNSS orbits and satellite clock corrections. Remote Sensing 12(14):2322, DOI:10.3390/rs12142322

Arnold D, Grombein T, Schreiter L, Sterken V, Jäggi A: Reprocessed precise science orbits and gravity field recovery for the entire GOCE mission.

Publication in preparation:

© ESA

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Summary

Solution Trend [cm/year]

Cosine [cm]

Sine [cm]

GOCE-GPS 1.27 1.44 1.37

GRACE-GPS 1.87 1.35 1.01

RMS values w.r.t.

ITSG-Grace2018

• Complete reprocessing of the GOCE Precise Science Orbits (PSO)

• Improved GPS-based gravity field recovery based on reprocessed PSO

• Time-variable gravity field recovery from reprocessed PSO

– Major time-variable signals can be recovered from about 4 years of GOCE-GPS data – Use of GOCE accelerometer data is crucial to derive meaningful linear trends

– Temporal variations obtained from GOCE are comparable to those from GRACE-GPS data

References

Jäggi A, Bock H, Meyer U, Beutler G, van den IJssel J (2015): GOCE: assessment of GPS-only gravity field determination. Journal of Geodesy 89(1):33–48, DOI:10.1007/s00190-014-0759-z Schreiter L, Arnold D, Sterken V, Jäggi A (2019): Mitigation of ionospheric signatures in Swarm GPS gravity field estimation using weighting strategies. Annales Geophysicae 37(1):111–127, DOI:10.5194/angeo-37-111-2019

Sušnik A, Grahsl A, Arnold D, Villiger A, Dach R, Beutler G, Jäggi A (2020): GOCE: Validation of the EGSIEM-REPRO GNSS orbits and satellite clock corrections. Remote Sensing 12(14):2322, DOI:10.3390/rs12142322

Arnold D, Grombein T, Schreiter L, Sterken V, Jäggi A: Reprocessed precise science orbits and gravity field recovery for the entire GOCE mission.

Publication in preparation:

Thank you for your attention

© ESA